What fixing to use?

[Stones]

As referenced in another thread, I have a Vent Axia Sentinel Kinetic Plus MVHR unit.  @Declan52 and I have both found the fixings used to secure the front and back covers to be next to useless, with each of us having broken fixing points.  Chimney nuts slide over the the plastic fixing points pictured, with longish M3 bolts (with a really annoying 4 blade windmill head) then passing through the chimney nuts. 

 

 

 

 

Setting aside the bolt heads as an issue, the biggest problem is the movement in the chimney bolts and trying to properly seat the bolts in when refitting the front panel after servicing the unit.  I would like to use a fixing nut that does not move/ is more robust.  In my mind an adaptor with threaded 7mm outer diameter (to fit through the hole), threaded 3 or 4 mm internal diameter would be perfect as I could secure the adaptor in place on the fixing point with a nut on the blind side so the fixing doesn't move.  Something like this:

 

Other options seem to be:

 

Jacknut

Rivnut

Small metal cavity fixing

Rubber wellnut / rivnut

Threaded insert held in place with nut on both sides

 

Anyone have any other bright ideas?

 

 

[DOIGAN]

Take it you need something to go over that bracket in the photo and allow a screw to go through it? If so what about spire clips?

[Stones]

@DOIGAN That's what the unit was supplied with.  In the end I opted to get some new spire clips (I called them chimney nuts above) and new machine screws with a Pozi2 head, and accept that I will end up replacing the spire clips as soon as they become loose.